Abstract
Verifiable random functions (VRF), proposed in 1999, and selectively convertible undeniable signature (SCUS) schemes, proposed in 1990, are apparently thought as independent primitives in the literature. In this paper, we show that they are tightly related in the following sense: VRF is exactly SCUS; and the reverse also holds true under a condition. This directly yields several deterministic SCUS schemes based on existing VRF constructions. In addition, we create a new probabilistic SCUS scheme, which is very compact. We build efficient confirmation and disavowal protocols for the proposed SCUS schemes, based on what we call zero-knowledge protocols for generalized DDH and non-DDH. These zero-knowledge protocols are built either sequential, concurrent, or universally composable.
